Direct Removal of Tritium from Mixture Gas by Alloy Getter with Functional Surfaces

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Tritium and deuterium coexist with helium and other impurities in exhaust gas from fusion reactor core. The separation of tritium from He and other gases is important task from the viewpoints of safety assessment and tritium economy. Direct removal of tritium by alloy getters with low equilibrium tritium pressure is safe and efficient method for tritium separation. The efficiency for tritium removal, however, can be degraded by poisoning by impurities such oxygen and carbon. The objective of the present project is to explore the surface modification technique to drastically improve the durability of getters against poisoning. ZrNi was selected as model material.Pd coating was carried out in 2001 with electroless plating technique. Specimen was exposed to argon gas containing H_2O, CO_2 and O_2, and degradation in deuterium absorption rate was examined at temperatures from 373 to 573 K. The durability against poisoning was significantly improved by Pd coating above 473 K. It should be emphasized that no significant degradation was observed for Pd coated specimen at 573 K, whereas the specimen without Pd coating was completely deactivated by 2 h exposure.In 2001, attention was focused on improvement of durability at lower temperatures. Sputter deposition was selected as new Pd coating technique. The activation behavior after exposure to air was examined to investigate the influence of surface impurities on absorption of hydrogen isotopes. The Pd coated specimen was activated by heating in vacuum at 423 K, whereas activation at 873 K was necessary for the specimen without Pd coating. This observation indicated that no stable oxide was formed at the surface of Pd coated specimen by exposure to air at room temperature. So, high durability at low temperature is expected.The mass analyzer purchased was used to analyze impurities in argon, deuterium and hydrogen gases.